Polycarbonate (PC) has an outstanding impact resistance, creep resistance, high to tensile strength, flexural strength, elongation and rigidity, and it can be subjected to the explosion of TV screens. Further, PC has a high heat resistance and cold resistance, and it can be used at the temperature between 100° C. minus and 140° C. Meanwhile, PC has a fine electrical property, low coefficient of water absorption and good light permeability. Specifically, the visible light transmission of PC can reach about 90% and can be colored with any kind of coloring agent. At present, the large-scale industrialization production mainly relates to the preparation of aromatic polycarbonates, which are currently the second largest engineering plastics in the world. Aromatic polycarbonates have a wide range of uses in the national economy, which can be used in plenty of fields, such as automobiles, electronics and electrics, architecture, office equipments, packaging, sports equipments, medical care, household articles, etc.
At present, the industrialization production of polycarbonate is primarily achieved by interfacial phosgenation process and melt transesterification process, wherein the quality of the product prepared by interfacial phosgenation process is significantly superior to that prepared by melt transesterification process. The interfacial phosgenation process refers to a process for preparing polycarbonate resin by separation and purification after the reaction of the phenoxide dissolved in an alkali metal aqueous solution with phosgene and inert organic solvent(s) (for example, methylene chloride) on an oil-water interface in the presence of an acid acceptor, such as, alkali metal hydroxide aqueous solution.
During the course of an interfacial polycondensation, the reaction rate between phosgene and phenolate negative ions is very fast, so the chloroformate groups will form quickly by the reaction on the oil-water interface. However, the reaction rate between chloroformate groups and phenolate negative ions is much slower, thus conventionally a certain quantity of tertiary amines (such as triethylamine) would be usually added into the reaction as a catalyst, thereby forming an adduct with the chloroformate group, which consequently enhancing the reaction rate between chloroformate groups and phenolate negative ions. Moreover, the introduction of the catalyst leads to adding further processing steps (such as washing with acids) during the washing and purifying steps of the reaction solution to remove the catalyst from the reaction solution for recycling use. On one hand, the introduction of catalyst adds further catalyst's processing procedures, such as prepare, feeding, removal and recovery procedures, which increasing the equipment cost. On the other hand, the introduction of catalyst would easily cause that small amount of catalysts remain in the final resin, while the basic amine-type catalyst would accelerate chain scission of ester bond in the product during the processing of product, thereby reducing the product quality.
U.S. Pat. No. 3,530,094 provides a technique for preparing polycarbonates by a tanks-in-series two-phase interfacial method, which employs a tanks-in-series reactor. Phosgenation reaction takes place in the first reaction kettle, and catalyst and capping agent are added into the second reaction kettle to perform a coupling reaction and an end-capping reaction, wherein the total residence time of the reaction being about 50 mins. Meanwhile, it is pointed out in the patent that the amount of chloroformate group is usually excessive during the interfacial polycondensation process for preparing polycarbonates, and the chloroformate group is finally converted into a phenolic hydroxyl group for end capping via an alkaline hydrolysis.
U.S. Pat. No. 3,674,740 provides a technique for preparing polycarbonates by a two-phase interfacial method which employs a plug flow tubular reactor. The tubular reactor has a series of connected sections with different sizes, wherein the sections with large internal tube diameters are residence time sections and the sections with smaller internal tube diameters are mixing sections. The mixing sections provide Reynolds numbers in the mixing sections greater than 2,000 and the catalyst is added during the reaction.
U.S. Pat. No. 5,258,484 provides a technique for preparing polycarbonates by interfacial polycondensation with a combination of plug flow and complete mixing flow, wherein an organic phase solution containing phosgene introduced therein is first mixed with sodium bisphenol salt solution via the tubular reactor and reacted, then the reaction mixture is introduced into a CSTR to perform a coupling reaction. After a prepolymerization reaction, a catalyst is added into the CSTR in an amount of about 0.25 mol % of the feeding amount of Bisphenol A.
U.S. Pat. No. 4,338,429 provides a method for adding a cationic emulsifier during a phosgenation process, wherein the emulsifier can be tetraalkylammonium salts, etc. Using emulsifier can effectively reduce the interfacial tension between the organic phase and the aqueous phase, and it is advantageous to form the emulsion and improve the stability of emulsion. However, the addition of such an emulsifier makes the subsequent separation and purification difficult and complicated.
U.S. Pat. No. 5,182,361 provides a two-step process for a continuous interfacial polycondensation, wherein the first step (i.e. the reaction of prepolymer) is carried out in a stirring vessel, and a polycondensation of the prepolymer with a chain stopper is carried out in a continuous tubular reactor consisting of static mixers to obtain a product.
Chinese patent No. 101775128 provides a preparation process for preparing a high-molecular-weight polycarbonate via a two-step method, wherein a phosgene is added step by step, thereby obtaining a large number of oligomers having both ends which are phenolate negative ions in the first step to reduce the interfacial tension and improve the emulsifying effect. After a prepolymerization reaction, a catalyst is added into the CSTR in an amount of about 0.3 mol % of the feeding amount of Bisphenol A.
Chinese Patent No. 102030895 provides a process for preparing polycarbonates by adding BPA-sodium salt via a two-step method, wherein BPA is added step by step during the process to reduce the consumption of alkaline solution in the reaction. After a prepolymerization reaction, a catalyst is added into the CSTR in an amount of about 0.3 mol % of the feeding amount of Bisphenol A.
The polymerization reaction to form a polycarbonate mainly occurs on an oil-water interface and the reaction process is essentially controlled by the mass transfer of the dispersed phase. It can be seen from the above patents that the traditional process usually employs a stirring vessel reactor or a tubular reactor, the micro-mixing effect thereof is generally poor, resulting in a larger average droplet diameter of the dispersed phase (the Sauter diameter is usually above several hundreds of microns). In addition, if no catalyst is added during the reaction, it will result in the phenomena such as, the finally obtained molecular weight being significantly low and a large number of chloroformate groups hydrolyzing.